The purpose of this research is threefold: 1) to determine the effect of PEG-rHu MGDF on the duration and severity of thrombocytopenia post PBPC transplantation; 2) to ascertain the minimum effective dose (MED) of PEG-rHuMGDF in the setting of PBPC transplantation; 3) to assess the safety of PEG-rHuMGDF when administered in combination with Filgrastim.